This invention relates generally to control of the flow of fluids, such as fluids intravenously infused into medical patients.
The infusion of intravenous fluid requires precise control over the volume of fluid infused and the infusion flow rate in accordance with preselected values and different types of flow controlling devices have heretofore been utilized to meet the relatively wide variation of flow requirements. The flow of fluid through such prior flow controlling devices is induced by two basic methods, one being a gravity feed method and the other a positive fluid displacement pump method.
The gravity feed type of flow controller is associated with a drip counting method of monitoring flow. Because of the variables involved, such as fluid viscosity, this type of flow controller is of limited use and subject to errors in the determination of flow rate data from which flow control may be exercised.
In an effort to obtain more precise flow control, particularly where fluid is to be administered at relatively higher infusion flow rates beyond the capability of gravity feed controllers, the pump induced flow type of controller is utilized. Many of the latter type of flow controller utilize a peristaltic pump to avoid the severe pulsation effects of piston pumps and the complex and costly valve systems required to cope therewith. However, the peristaltic pumps also have certain drawbacks, such as unsteady flow rate making them unsuitable for delivery of fluid at low flow rates in spite of valving systems devised to cope with the unsteady flow characteristics.
In general, flow controllers utilizing peristaltic pumps have been devised in cassette form, having access doors and front panels mounting membrane key pads, operational status indicators, readout data displays and alarm devices. Such cassettes encompass flow meters as well as other expedients generally known in the art, such as cassette code identifying detectors, malfunction sensors, etc.
As a result of the aforementioned drawbacks associated with known flow controllers, it has been necessary to sometimes change the type of flow controller deemed desirable for intravenous administration, with a consequential interruption in fluid infusion to the patient. Further, because of the difficulties encountered in measuring both low and high flow rates, the flow meter has been eliminated from some flow controllers because of costs and lack of reliability. Additionally, prior flow controllers were unable to provide for rapid change in the source of fluid, between primary and secondary reservoirs, for example.
It is, therefore, an important object of the present invention to provide an infusion flow controller system through which flow of the fluid may be induced from selected reservoirs alternatively by gravity feed and pump displacement through operational mode selection without any installational change.
Another object in accordance with the foregoing object is to provide the infusion flow controller system with a flow meter capable of monitoring flow under either operational mode to provide accurate flow volume and rate data for display and for flow adjustment so as to achieve steady flow conditions.
Other objects in association with the foregoing objects include the detection of errors, malfunctions and the monitoring of operational modes peculiar to the unique attributes of the infusion flow controller system of the present invention.